Phase-selective a.c. adsorptive stripping voltammetry of lumazine on a hanging mercury drop electrode

The electrochemical behavior of lumazine (LMZ), an important antibacterial agent, has been studied at the hanging mercury drop electrode (HMDE). The nature of the process taking place at the HMDE was clarified. Its adsorption behavior at HMDE has been studied by using a.c and cyclic voltammetry (CV). Both the molecule and its reduced product appeared to be adsorbed at the surface of the electrode. Controlled adsorptive accumulation of LMZ on the HMDE provides the basis for the direct stripping measurement of that compound in the subnanomolar concentration level. Experimental and instrumental parameters for the quantitative determination were optimized. Phase-selective a.c voltammetry provided the best signal and gave a detection limit of 0.15 μg L^–1 (9.0 × 10^–10 mol/L) LMZ in aqueous solution. Molecules or ions which may interfere were studied.     

Determination of secnidazole in urine by adsorptive stripping voltammetry

Cyclic voltammetry was used to explore the adsorption behavior of secnidazole on a hanging mercury drop electrode (HMDE). The effects of various operational parameters on the accumulation behavior of the adsorbed species were tested. Thus, a sensitive stripping voltammetry procedure for the determination of secnidazole with an adsorptive accumulation on the surface of HMDE has been developed. Measurements were taken by differential-pulse voltammetry after determination of the optimum conditions. The linear concentration range was 1 x 10(-8)-1 x 10(-7) s when using a 120 s preconcentration at -0.1 V vs. Ag/AgCl in acetate buffer of pH 4.0. The detection limit of secnidazole was 5 x 10(-9) M. The precision, expressed by the coefficient of variation, was 2.5% (n = 10) at a concentration of 1 x 10(-7) m. The method was successfully applied to the analysis of secnidazole in urine.     

Cathodic adsorptive stripping square-wave voltammetry of the anti-inflammatory drug meloxicam

The adsorptive behavior of the anti-inflammatory drug meloxicam was studied by cyclic, differentia-pulse and square-wave voltammetry on a hanging mercury drop electrode (HMDE). The drug was accumulated at HMDE and a well-defined stripping peak current was obtained at -1.42 V vs. Ag/AgCl (saturated KCl) electrode in acetate buffer solution (pH 5.0). A voltammetric procedure was developed for the determination of meloxicam using square-wave cathodic adsorptive stripping voltammetry (SW-CASV). The optimum working conditions for the determination of the drug were established. The analysis of meloxicam in human plasma was carried out satisfactorily.     

Determination of the pesticide Chlorpyrifos by cathodic adsorptive stripping voltammetry

The adsorption behavior and differential pulse cathodic adsorptive stripping voltammetry of the pesticide Chlorpyrifos (CP) were investigated at the hanging mercury drop electrode (HMDE). The pesticide was accumulated at the HMDE and a well-defined stripping peak was obtained at –1.2 V vs Ag/AgCl electrode at pH 7.50. A voltammetric procedure was developed for the trace determination of Chlorpyrifos using differential pulse cathodic adsorptive stripping voltammetry (DP-CASV). The optimum working conditions for the determination of the compound were established. The peak current was linear over the concentration range 9.90 × 10^–8– 5.96 × 10^–7 mol/L of Chlorpyrifos. The influence of diverse ions and some other pesticides was investigated. The analysis of Chlorpyrifos in commercial formulations and treated waste water was carried out satisfactorily     

镓(Ⅲ)-茜素红体系的吸附伏安法

本文对镓(Ⅲ)与茜素红络合物在悬汞电极上的吸附伏安法作了研究,确定了电极过程.在HAc-NH_4Ac(pH4.06)缓冲溶液中茜素红存在下,用1.5阶微分吸附伏安法测定镓,其线性范围是1×10~(-10)～1×10~(-7)mol/L,其检测限为1×10~(-10)mol/L,并用此法测定了中草药中的痕量镓.     

The experimental and theoretical QM/MM study of interaction of chloridazon herbicide with ds-DNA

We report a multispectroscopic, voltammetric and theoretical hybrid of QM/MM study of the interaction between double-stranded DNA containing both adenine-thymine and guanine-cytosine alternating sequences and chloridazon (CHL) herbicide. The electrochemical behavior of CHL was studied by cyclic voltammetry on HMDE, and the interaction of ds-DNA with CHL was investigated by both cathodic differential pulse voltammetry (CDPV) at a hanging mercury drop electrode (HMDE) and anodic differential pulse voltammetry (ADPV) at a glassy carbon electrode (GCE). The constant bonding of CHL-DNA complex that was obtained by UV/vis, CDPV and ADPV was 2.1×10(4), 5.1×10(4) and 2.6×10(4), respectively. The competition fluorescence studies revealed that the CHL quenches the fluorescence of DNA-ethidium bromide complex significantly and the apparent Stern-Volmer quenching constant has been estimated to be 1.71×10(4). Thermal denaturation study of DNA with CHL revealed the ΔTm of 8.0±0.2°C. Thermodynamic parameters, i.e., enthalpy (ΔH), entropy (ΔS°), and Gibbs free energy (ΔG) were 98.45 kJ mol(-1), 406.3 J mol(-1) and -22.627 kJ mol(-1), respectively. The ONIOM, based on the hybridization of QM/MM (DFT, 6.31++G(d,p)/UFF) methodology, was also performed using Gaussian 2003 package. The results revealed that the interaction is base sequence dependent, and the CHL has more interaction with ds-DNA via the GC base sequence. The results revealed that CHL may have an interaction with ds-DNA via the intercalation mode.     

Differential pulse cathodic stripping voltammetry of the copper complexes of glycyl-L-histidyl-glycine at a hanging mercury drop electrode

The behaviour of the copper complexes of glycyl-L-histidyl-glycine (GHG) was investigated using cyclic voltammetry and differential pulse voltammetry after their adsorptive accumulation on the surface of a hanging mercury drop electrode (HMDE). The nature of the observed cathodic and anodic peaks was established and optimum conditions were found for the differential pulse cathodic stripping voltammetric detemination of GHG at the 1 x 10(-8)M concentration level using adsorptive accumulation at -0.20 V vs. Ag/AgCl reference electrode and the cathodic stripping peak around -0.4 V (pH 8.3). This peak corresponds to the reduction of the Cu(I)-GHG complex formed at the HMDE surface as an intermediate in the reduction of Cu(II)-GHG to Cu(O)amalgam.     

Determination of the pesticide Chlorpyrifos by cathodic adsorptive stripping voltammetry

The adsorption behavior and differential pulse cathodic adsorptive stripping voltammetry of the pesticide Chlorpyrifos (CP) were investigated at the hanging mercury drop electrode (HMDE). The pesticide was accumulated at the HMDE and a well-defined stripping peak was obtained at –1.2 V vs Ag/AgCl electrode at pH 7.50. A voltammetric procedure was developed for the trace determination of Chlorpyrifos using differential pulse cathodic adsorptive stripping voltammetry (DP-CASV). The optimum working conditions for the determination of the compound were established. The peak current was linear over the concentration range 9.90 × 10^–8– 5.96 × 10^–7 mol/L of Chlorpyrifos. The influence of diverse ions and some other pesticides was investigated. The analysis of Chlorpyrifos in commercial formulations and treated waste water was carried out satisfactorily Received: 10 July 1997 / Revised: 1 April 1998 / Accepted: 6 April 1998     

核黄素丁酸酯在汞电极上的吸附伏安特性及其反应速率常数的测定

循环伏安法表明,在ＮａＯＨ底液中核黄素丁酸酯（ｒｉｂｏｆｌａｖｉｎｅ　ｔｅｔｒａｂｕｔｙｒａｔｅ,ＲＴ）在汞电极上有一对氧化还原峰,其峰电位Ｅｐｃ＝Ｅｐａ＝－０．６４Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）。本文用多种电化学手段对ＲＴ的吸附特性进行了较详细的研究。吸附粒子为ＲＴ中性分子,测得ＲＴ在汞电极上的饱和吸附量为５．４２×１０－１１ｍｏｌ／ｃｍ２,每个ＲＴ分子所占电极面积为３．０６ｎｍ２,ＲＴ在悬汞电极上的吸附符合Ｆｒｕｍｋｉｎ等温式。测得吸附系数β＝４．６×１０５,吸引因素γ＝ １． １０,吸附自由能△Ｇ°＝－ ３２． ３０ ｋＪ／ｍｏｌ。本文还用循环伏安法研究了ＲＴ的电极反应动力学性质,测定了其在汞电极上的反应速率常数。     

Simultaneous determination of tin and lead by a.c. anodic stripping voltammetry at a hanging mercury drop electrode sensitized by cetyltrimethylammoniu

The influence of cetyltrimethylammonium bromide (CTAB) on the simultaneous determination of tin(IV) and lead(II) by anodic stripping voltammetry at a hanging mercury drop electrode (HMDE) in a 0.1 M hydrochloric acid—0.1 M oxalic acid medium was studied using d.c. and a.c. stripping. In the presence of CTAB, tin and lead show voltammetric peaks separated by 100 mV, the sensitivity depending on the concentration of CTAB. The best conditions for the simultaneous determination of both elements (2 × 10^-3 M) were found. A method is proposed for the determination of tin in the presence of lead and three procedures are given for the determination of lead in the presence of tin.     

Validated polarographic methods for the determination of certain antibacterial drugs.

Two simple, precise, inexpensive and sensitive voltammetric methods for the determination of lomefloxacin (LFX), sparfloxacin hydrochloride (SFX), gatifloxacin (GFX), and moxifloxacin (MFX) were developed. The present methods were first used to explore the adsorption behavior of the four investigated antibacterial agents at a hanging mercury dropping electrode (HMDE), by a direct method and secondly by a modification via their complexation with PdCl(2). For the direct method, drugs were accumulated on HMDE, and a well-defined reduction peak was obtained in Britton-Robinson buffer of pH 7 for LFX and SFX, and pH 6 for GFX and MFX. The adsorptive stripping response was evaluated as a function of some variables such as the scan rate, pH, accumulation time and potential. For the modified method, the adsorptive behavior of Pd(II)-4-quinolone complexes at the HMDE developed a strippining voltammetry peak at a more negative potential than that of the free Pd(II) ions (-1.05 V). The limits of detection (LOD) were 2 x 10(-8) M, while the limits of quantification (LOQ) were 6 x 10(-8) M for the investigated drugs. The methods were applied to the determination of LFX, SFX, GFX, and MFX in biological samples and pharmaceutical preparations, and also compared with the official reference methods. Complete validation of the proposed methods was also done.     

依沙吖啶在玻碳电极上的阳极伏安行为

用直流伏安法（DCV）、微分脉冲伏安法（DPV）和循环伏安法（CV）在玻璃电极（GCE）上研究了依沙吖啶（EAD）在不同介质中的阳极伏安行为，发现在0．1mol/L氢氧化钠溶液中于0．38V（vs.Ag/AgCl)左右产生一个良好的阳极氧化峰，浓度在0．05－80mg/L之间与其峰电流呈线性关系，用本法不需要分离，可直接测定药物制剂和加标尿样，RSD为1．4％－2．7％(n=10)。尿样中EAD的回收率为89％－95％。探讨了EAD在GEC上的电极反应机理。     

尿酸在生物分子修饰电极上的伏安测定

采用循环伏安法制备了聚L-苯丙氨酸薄膜修饰玻碳电极,研究了尿酸在该修饰电极上的电化学行为,建立了循环伏安法测定尿酸的新方法。研究发现：在pH 5.6的磷酸盐缓冲溶液中,尿酸在聚L-苯丙氨酸修饰电极上于0.43V处产生一灵敏的氧化峰,应用循环伏安法测定其氧化峰电流与尿酸的浓度在2.0×10-6～3.0×10-4 mol/L呈良好的线性关系,检出限为1×10-6 mol/L。对1.0×10-5 mol/L尿酸平行测定5次,相对标准偏差为3.0％。该生物分子电极制作简单,重现性好,可用于尿液中尿酸的测定,结果令人满意     

Amperometric determination of glutathione and cysteine on a Pd-IrO(2) modified electrode with high performance liquid chromatography in rat brain microdialysate

A Pd/IrO(2) co-electrodeposited glassy carbon electrode was prepared and the electrochemical behavior of glutathione (GSH) at this chemically modified electrode (CME) has been studied by cyclic voltammetry (CV). The results indicated that the modified electrode efficiently exhibited electrocatalytic oxidation for GSH with relatively high sensitivity, stability, and long-life. Coupled with high-performance liquid chromatography (HPLC), the Pd/IrO(2) modified electrode was utilized for the electrochemical detection (ECD) of the thiocompounds, glutathione and cysteine (Cys). The peak currents were linear with the substance concentrations in the range of 1.0 x 10(-5) mol L(-1) to 8.0 x 10(-4) mol L(-1) for GSH and 4.0 x 10(-6) mol L(-1) to 2.0 x 10(-4) mol L(-1) for Cys. The detection limits were 2.0 x 10(-6) mol L(-1) for GSH and 5.0 x 10(-7) mol L(-1) for Cys with S/N of 3. The method has been successfully applied to assess the contents of GSH and Cys in rat brain microdialysates.     

Electrochemical determination of methimazole based on the acetylene black/chitosan film electrode and its application to rat serum samples

A novel method has been developed for the determination of methimazole, which was based on the enhanced electrochemical response of methimazole at the acetylene black/chitosan composite film modified glassy carbon electrode. The electrochemical behavior of methimazole was studied at this film electrode by cyclic voltammetry and differential pulse voltammetry. The experimental results showed that methimazole exhibited a remarkable oxidation peak at 0.63V at the film electrode. Compared with the bare glassy carbon electrode, the oxidation peak current increased greatly, and the peak potential shifted negatively, which indicated that the acetylene black/chitosan film electrode had good catalysis to the electrochemical oxidation of methimazole. The enhanced oxidation current of methimazole was indebted to the nano-porus structure of the composite film and the enlarged effective electrode area. The influences of some experimental conditions on the oxidation of methimazole were tested and the calibration plot was examined. The results indicated that the differential pulse response of methimazole was linear with its concentration in the range of 1.0×10(-7) to 2.0×10(-5)mol/L with a linear coefficient of 0.998, and in the range of 4.0×10(-5) to 3.0×10(-4)mol/L with a linear coefficient of 0.993. The detection limit was 2.0×10(-8)mol/L (S/N=3). The film electrode was used to detect the content of methimazole in rat serum samples by the standard addition method with satisfactory results.     

Electrochemical detection of parathion at a glassy-carbon electrode modified with hexadecane

A modified electrode, based on a hexadecane (C(16))-coated glassy-carbon electrode (GCE) has been developed for the determination of parathion. The electrochemical behavior of parathion was investigated by cyclic voltammetry (CV). The peak potential and peak current were found to depend on the supporting electrolyte and the pH of the buffer solution. The reduction currents for parathion were proportional to parathion concentration over the range 8x10(-8)-2x10(-5) mol L(-1). The detection limit was 2x10(-8) mol L(-1) parathion for an accumulation time of 30 s. The effects of organic and inorganic species on the determination of parathion were also studied. A procedure was developed to extract parathion from spiked soil samples using a mixture of dichloromethane and acetone as the extraction solvent. The complete extraction and analytical procedure are simple, inexpensive and rapid. Parathion was determined in a soil sample by use of linear scan voltammetry (LSV).     

Adsorptive stripping voltammetric behaviour of mitoxantrone on mercury electrodes

The electrochemical behaviour of mitoxantrone (MXT), an important antineoplastic agent, has been studied at mercury electrodes. The nature of the process taking place at the hanging mercury drop electrode (HMDE) was clarified. The electrochemical behaviour observed was in close agreement with theoretical predictions for an adsorbed molecule which is reversibly reduced. Both the molecule and its reduced product appeared to be adsorbed at the surface of the electrode. Adsorptive stripping voltammetry has been proven to be advantageous over any other assay technique, allowing 5 x 10(-11)M MXT to be detected. The interference arising from surfactants competing for the adsorption sites at the electrode have been studied and the possibility of MXT determination in dilute urine samples has been shown. Some interesting data, such as the MXT adsorbing surface area and the kinetic constant of the associated coupled chemistry reaction were also determined.     

Homogeneous and nanomolar detection of hydrazine by indigocarmine as a mediator at the surface of TiO2 nanoparticles modified carbon paste electrode

The homogeneous electrocatalytic oxidation of hydrazine（HZ） has been studied by indigocarmine（IND） as a mediator at the surface of TiO₂ nanoparticles modified carbon paste electrode（TNMCPE）.Cyclic voltammetry was used to study the electrochemical behavior of IND at different scan rates.The voltammetric response of the modified electrode was linear against the concentration of HZ in the ranges of 3.0×l0^-8-7.0×10⁶ mol/L with differential pulse voltammetry method.The detection limit（3σ） was determined as 27.3 nmol/L.To evaluate the applicability of the proposed method to real samples,the modified CPE was applied to the determination of HZ in water samples.     

舒乐安定吸附伏安法的研究

Jimenez曾研究了舒乐安定的性质,但灵敏度较低,本文提出了测定痕量舒乐安定的吸附伏安法,在0.1 mol/L NH_3-NH_4Cl溶液(pH 9.3)中,富集电位—0.80 V(us. Ag/AgCl)得一灵敏的舒乐安定还原峰,Ep=—1.05 V,i_p与舒乐安定浓度在3.0×10~(-9)～5.0×10~(-6) mol/L范围内呈线性关系,检测限达1.0×10~(-9)mol/L,并用于试样的测定,用循环伏安法和恒电     

Determination of ketorolac in human serum by square wave adsorptive stripping voltammetry

The adsorption behavior of ketorolac on a hanging mercury drop electrode (HMDE) was explored by square-wave and cyclic voltammetry. The square wave voltammetric response of ketorolac depends on the parameters of the square wave voltammetry excitation signal as well as on the pH of the medium and the accumulation time. The drug was accumulated at HMDE and a well-defined peak was obtained at -1.41 V versus. Ag/AgCl (saturated KCl) in acetate buffer of pH 5.0. A square-wave adsorptive stripping voltammetric method for the quantitative determination of ketorolac was developed. The linear concentration range was 1x10(-10)-1x10(-8) when using 300 s accumulation at -0.8 V. The detection limit of ketorolac was 1.0x10 (-11)M . The precision was excellent with relative standard deviation of 3.85% at concentration of 5x10 (-8)M after 60 s accumulation time. Applicability to serum samples was illustrated. A detection limit of 14 ng per ml of serum was obtained.